Senate Democrats are looking to build firewalls between their legislation reauthorizing transportation programs and the Keystone XL pipeline, which House Republicans will push hard for in the upcoming conference committee. And Republicans will likely have an ally on Keystone in a Democratic conferee, Senate Finance Chairman Max Baucus (Mont.).

Senate Majority Leader Harry Reid (D-Nev.) and Minority Leader Mitch McConnell (R-Ky.) appointed conferees Tuesday, and their House counterparts are expected to do the same today. But the path to approving a final bill is unclear and rocky. The Senate passed its two-year legislation on a 74-22 bipartisan vote. The House struggled for months to arrive on a legislative vehicle, finally approving a short-term extension last week just to get to conference.

“Our bill is so good, it’s just astounding. It’s got so much safety stuff in it. It’s got money in it,” said Senate Commerce Chairman Jay Rockefeller (D-W.Va.), a conferee. “Theirs ... has no money. It’s not comparable.”

The House included in its measure language fast-tracking the pipeline. President Barack Obama has already threatened to veto any transportation legislation that includes such language. The pipeline has Democratic support in both chambers, but none as powerful as Baucus’.

In a payroll conference committee earlier this year, Baucus worked counter to leadership and the administration, negotiating ways to approve the pipeline and engaging in talks with Sen. John Hoeven (R-N.D.), who was named to the conference committee by McConnell on Tuesday.

Senate Democrats might have some cushion among their ranks, however. Leaders agreed to a larger conference, and Senate Democrats on the committee outnumber Republicans, 8-6, leaving room for Baucus to defect over the pipeline and to not jeopardize Democratic approval.

Fighting over Keystone has become part of the game during the past few months. Republicans have brought construction of the pipeline into several legislative fights. They have used it to criticize the administration, which has an expedited request to consider the pipeline once this year, by linking it to job creation.

Reid said he, like the president, is unmoved by Republican arguments on the issue.